Question

A cistern $6m$ long and $4m$ wide contains water up to the depth of $1m25cm$. The total area of the wet surface is :

• A. $49m^2$
• B. $50m^2$
• C. $53.5m^2$
• D. $55m^2$

Answer 1

The correct option is A $49m^2$

Area of wet surface = $2(lb+bh+hl)-lb$

We subtracted $\left(lb\right)$ term because we do not have to take upper surface of cuboid

$\therefore$ Area of wet surface $=2(lb+bh+hl)-lb$

$=2(bh+hl)+lb$

$=2(4\times 1.25+6\times 1.25)+6\times 4$

$=2(5+7.5)+24$

$=25+24$

$=49m^2$

Total area is $49m^2$